This is a question about what ES does or doesn't do with shards/
- a box/node with specific shard/replica allocation filtering goes
- a new box is added to the cluster in order to replace the downed
box from 1)
Consider, for example, a cluster of 4 boxes:
- box #1 hosts shard #1
- box #2 hosts shard #2
- box #3 hosts replica of shard #1
- box #4 hosts replica of shard #2
Assume allocation awareness was used to "tag" the above boxes/nodes in
order to maintain full control over where ES should place shards and
replicas for our Foo index.
A) What happens when box #4 dies?
Does ES automatically replicate under-replicated shards?
I think the answer is No, but in case ES does automatically re-
replicate, where would it place a new replica of shard #2 in this
B) Same questions as above, but for box #2 going down? (In other
words, the box that dies is the one with the original shard, not its
I think the answer should be the same as for A), but want to
C) If box #4 dies and ES doesn't automatically allocate replica of
shard #2 (which was on that box) to another box, what should an admin
do in order to preserve the same shard & replica allocation as before?
In other words, if he wants to remain in full control of
allocation and maintain order and control over what is placed where,
what are the steps he should follow?
D) Related to C - if an admin adds a new box to the cluster - a box
meant as a replacement for box #4, but not yet tagged with allocation
awareness stuff - will ES automatically "grab" it and start putting
new shards on it?
In other words, if the admin just adds a "blank" box to the
cluster, will he lose control over what ES will put there because ES
could start using it right away?
E) Related to D - what should the admin do when adding a new box #4
replacement to the cluster?
Does he have to make sure he applies allocation awareness stuff to
this new box before it's added to the cluster?
Does he have to make some explicit calls to ES to tell it "Hey, I
made this new box #4 available for you and it's allocation aware - now
go and create a replica of shard #2 on it"?
Sorry for all these questions, but hopefully others will find this
useful, too. Thanks!
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